Integrated circuit devices continue to be reduced in size in order to create smaller devices that consume less power and operate faster. However, the reduction in size has increased the need for more precise layers that form the integrated circuits. More precise layers require excellent step coverage to prevent unwanted shorts between layers in an integrated circuit. That is, the stoichiometry of the layers must continue to be improved. Moreover, the purity of the layers becomes more important on the smaller scale integrated circuits as a single impurity may cause a layer to fail or short two adjacent layers.
As an example, modem integrated circuit design has advanced to the point where line width may be 0.25 microns or less. As a result, repeatability and uniformity of processes and their results is becoming increasingly important. Generally, it is desired to have thin films deposited on the wafer to save space. Yet reducing the thickness of films can result in pinholes and reduced mechanical strength, both of which may lead to shorts through the film.
Another development in the field of thin film technology for coating substrates is atomic layer deposition (ALD). A description of ALD is set forth in U.S. Pat. No. 5,879,459, which is herein incorporated by reference in its entirety. ALD operates by confining a wafer in a reaction chamber at a typical temperature of less than 300 degrees Celsius. Precursor gas is pulsed into the chamber, wherein the pulsed precursor forms a monolayer on the substrate by chemisorption. The low temperature limits the bonding of the precursor to chemisorption, thus only a single layer, usually only one atom or molecule thick, is grown on the wafer. Each pulse is separated by a purge pulse which completely purges all of the precursor gas from the chamber before the next pulse of precursor gas begins. Each injection of precursor gas provides a new single atomic layer on the previously deposited layers to form a layer of film. Obviously, this significantly increases the time it takes to deposit a layer having adequate thickness on the substrate.
These and other embodiments, aspects, advantages, and features of the present invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art by reference to the following description of the invention and referenced drawings or by practice of the invention. The aspects, advantages, and features of the invention are realized and attained by means of the instrumentalities, procedures, and combinations particularly pointed out in the appended claims.